Plastic bags are typically made from cut plastic sheets. In many cases lasers are utilized to cut plastic sheets and weld them together. Specifically, CO2 lasers are almost universally utilized to weld and cut plastic materials. The rapid absorption of the laser energy produced in this configuration (10.6 μm) makes this an efficient system for this application. It is known that by varying the focus and dwell time of the laser, it is possible to cut, mark or weld thermoplastic materials.
However, there are problems associated with using the aforementioned laser to cut and weld plastic materials to form bags and assemblies. First, some prior art devices require that the film sheets must be oriented in the vertical plane. This makes it very difficult to support large sheets, and it is doubtful that the distance between the sheets and the laser can be practically maintained to the tight tolerances required in order not to burn or damage portions of the seam to be welded. The vertical orientation makes it impossible to support ports or other fixtures that may need to be attached to the sheets.
The aforementioned system requires dual laser sources—one on either side of the two sheets. In other systems, a complex beam splitter assembly is needed to weld and cut thermoplastic materials. It also requires the use of two air jets—one on each side of the two sheets—to force the sheets into an intimate contact needed for effective welding. Such a two-air-jet system complicates the manufacturing process, since it is difficult to maintain focus of the two laser beams in order to achieve consistent welding or cutting. Two laser systems also require special optics to prevent the laser beam of one laser coupling back into the other laser damaging it.
Next, another plastic bag forming device utilizes a vacuum hold-down table and a single laser that can be moved around the table to perform the cutting and welding operations. It uses a frame or rollers to stretch the sheets to be welded in intimate contact. A disadvantage with this invention is that the sheets tend to become distorted during the stretching, and may cause wrinkles in the finished product, and this method requires the use of heated rollers and platens. More importantly, the framing method and apparatus limits the size of the bag or assembly that can be manufactured, as very large sheets cannot be effectively tensioned so that the contact is maintained consistently across the entire sheet. In some new applications, especially bags for cell culture, there is a need to make large bags that can easily exceed 6 by 10 feet in size.
Another problem with laser cutting of clear films is the tendency of vaporized film particles to redeposit onto the film surface. This leads to an unsightly appearance not suitable for the manufacture of pharmaceutical products. A major limitation of other prior art devices is that they are restricted to two dimensional or planar assemblies. It is often desirable to weld thermoplastic sheets to form three dimensional structures. To do so requires a welding method and apparatus that has a small weld zone through which the sheets to be welded may be moved freely in any direction without any restriction imposed by fixturing frames.
Therefore, there is a need for a system that allows a user to maintain consistent welding and cutting to simply form a bag or assembly. Also, there is need for a system that allows a user to make a large bag that can easily exceed 6 by 10 feet in size.